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Abstract

Pd4Br4Te3 was prepared from Pd, Te, and PdBr2 at 700 K. Its structure was determined by single-crystal X-ray diffraction to be triclinic, P , Pearson symbol aP22; a=842.5(2), b=845.0(3), c=864.8(3) pm; =82.55(3), =73.36(2), =88.80(2)°; Z=2. The Br and Te atoms are arranged according to the motif of cubic closest-packed spheres in which every 15th position is vacant; the Pd atoms occupy 8/15 of the octahedral voids. The symmetry relations with the packing of spheres are derived. Prominent structural units are hollow cuboctahedral [(PdBrTe)6] units, the Pd atoms are positioned near the centers of the square faces of the Br6Te6 cuboctahedra; the cuboctahedra and double-octahedral Pd2Br4Te6 units are connected to strands by sharing triangular Te3 faces. The strands are condensed by common Br atoms into layered assemblies. Conspicuously close Te Te contacts in the Te3 triangles indicate attractive Te Te interactions. The valence puzzle is resolved by the formula Pd(+II)4Br(-I)4Te(-4/3)3. Positive Te Te Mulliken orbital populations and the Pd K, Br K, and Te LIII XANES spectra of Pd4Br4Te3 referenced to the spectra of PdBr2, K2PdBr6, PdTe, and PdTe2 are in accord with attractive Te Te interactions. The measured semiconducting and diamagnetic properties are compatible with the derived picture of chemical bonding in Pd4Br4Te3.